1. Field of the Invention
This invention generally relates to selecting one or more parameters for inspection of a wafer. Certain embodiments relate to selecting one or more parameters for a multi-test inspection of a wafer given one or more optical modes.
2. Description of the Related Art
The following description and examples are not admitted be prior art by virtue of their inclusion in this section.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers. Inspection for many different types of defects has become more important recently. In some instances, a system that is configured to detect different types of defects may have adjustable output acquisition and sensitivity (or defect detection) parameters such that different parameters can be used to detect different defects or avoid sources of unwanted (nuisance) events. For instance, the spot or pixel size, wavelength, aperture, focus offset, polarization, or angles of collection may be different for an inspection process used to detect particulate defects than for an inspection process used to detect scratches.
Although an inspection system that has adjustable output acquisition and sensitivity parameters presents significant advantages to a semiconductor device manufacturer, these inspection systems are essentially useless if incorrect output acquisition (e.g., data, signal, and/or image acquisition) and/or sensitivity parameters are used for an inspection process. For example, incorrect or non-optimized output acquisition parameters may produce such high levels of noise that no defects of interest (DOI) can be detected in the generated output, in addition, since the defects, process conditions, and noise on a wafer may vary dramatically, the best output acquisition and sensitivity parameters for detecting the defects on a particular wafer may be difficult, if not impossible, to predict. Therefore, although using the correct output acquisition and sensitivity parameters will have a dramatic effect on the results of inspection, it is conceivable that many inspection processes are currently being performed with incorrect or non-optimized output acquisition and/or sensitivity parameters.
The task of setting up an inspection process for a particular wafer and a particular DOI may be extremely difficult for a user particularly when an inspection system has a relatively large number of adjustable output acquisition settings and sensitivity parameters. However, most inspection processes are currently set up using a large number of manual processes (e.g., manually selecting the output acquisition parameters, manually analyzing the inspection results, etc.). As such, setting up the inspection process may take a relatively long time. Furthermore, depending on the types of wafers that will be inspected with the inspection system, a different inspection process may need to be set up for each different type of wafer. Obviously, therefore, setting up the inspection processes for all of the different wafers that are to be inspected may take a prohibitively long time.
Furthermore, it may be desirable to perform inspection of wafers using a multi-pass or multi-scan inspection process. Different parameters for inspection may be used for each pass or scan. One currently used method for multi-pass inspection setup is to set up the multiple scans individually. While parts of the setup may be common among scans such as light level training and Fourier filter training, often the parameters for each scan are independent of the other scans' parameters and must be optimized separately. The major, time consuming effort is in two areas, optics selection and defect detection algorithm parameter optimization.
To perform optics selection in the above-described setup method, the user selects a combination of optical modes based on the signal-to-noise ratio (S/N) of a selected set of defects, which includes both DOI and nuisance. The S/N for each defect is collected from individual optical modes and is listed in a table. The user then analyzes the table contents in order to pick the best optical modes, typically those with high S/N for DOI and low S/N for nuisance.
For the algorithm parameter optimization step, the user tunes the detection algorithm parameters for each scan to maximize the DOI capture and minimize nuisance/noise capture on the inspection system or with the assistance of optimization tools a sensitivity tuner) after the user classifies samples of detected detects through optical or scanning electron microscope (SEM) review. The result is the optimized set of algorithm parameters for each individual scan. If the user needs to coordinate the scans for further optimization, such optimization can involve intensive data analysis. Sometimes engineering efforts, such as software development, are necessary for such optimization due to its complexity or sheer number of combinations under consideration.
The method described above has a number of disadvantages. For example, the method described above for multi-pass inspection setup is substantially labor intensive. Given the flexibility and complexity that most advanced inspection systems offer, there are typically substantially large numbers of optical mode combinations one can explore. Often, if a single inspection scan cannot provide the required DOI sensitivity and/or nuisance capture rate, the user cannot afford the time to consider combinations of optical modes and perform multiple passes of sensitivity parameter tuning. In addition, simply combining the results from individually optimized scans may not lead to optimal inspection results. To achieve the best inspection results, multiple scans need to work together in a complementary fashion to detect as many DOI and suppress as many nuisances as possible. Due to limited time and capability of optimization tool sets, these multi-pass options cannot be adequately explored often resulting in sub-optimal inspection outcomes.
Accordingly, it would be advantageous to develop methods and/or systems for selecting one or more parameters for inspection of a wafer that are less labor intensive, quicker, and less tedious than previously used methods and can be used to select one or more parameters for a multi-pass or multi-scan inspection that are more suitable, or even optimal, for the inspection than parameters of multi-pass or multi-scan inspections selected using the method described above.